This invention relates to the preparation of polymer materials and a method of making those materials. Examples of such materials include, but are not limited to coated fabrics, extruded wire cables, pipes, blow-molded articles, etc.
There are a variety of procedures currently used to produce textiles coated with polymer based materials. Among these are spread coating, melt calendaring, and extrusion. Spread coating is particularly applicable to vinyl plastisol systems.
There are problems with materials made by spread coating of polyvinyl chloride (PVC) plastisol. They include difficulties stemming from the fact that these systems contain a liquid and that these systems are based on PVC. A system that contains a liquid plasticizer is subject to plasticizer loss from exudation, evaporation, or extraction. Such loss can reduce the physical properties of the coated fabric and result in a brittle material that is prone to cracking. The loss can also produce problems because of the presence of the escaped plasticizer. An example of this is the buildup of plasticizer on the interior surfaces of automobile windows in cars that are exposed to higher than ambient temperature. The presence of PVC in fabric systems can be detrimental. For example the hydrochloric acid generated by PVC in a fire can be detrimental. PVC containing materials are therefore excluded from certain applications.
The present invention allows for a coating material that can be applied in a manner similar to PVC spread coatings. The resulting fabric system, after curing, has no liquid component that could migrate or be extracted. It is also free of halogens and would not produce hydrochloric acid upon combustion. In addition, these new polymer products of the present invention would have enhanced physical and chemical properties relative to a PVC plastisol based system. Such improvements would include any combination of low temperature flexibility, weatherability, tensile properties (such as tensile strength at break, percent elongation at break, and tensile yield strength as measured in accordance with ASTM test method D638), abrasion resistance, and compression set (as measured by ASTM test method 395B).
Another important advantage of the system of the present invention is that with only modest modifications it can be run on a PVC plastisol coating line. This permits manufacturers of coated fabrics to use this new technology in their current production lines without major equipment modifications. The modest modifications needed would be in the area of preparing the casting fluid and in the temperature of the spread coating step.
Melt calendering is conventionally used in the application of polymeric coatings to fabrics. The current invention provides significant advantages over conventional polymeric coatings in that process both in terms of processing advantages and in enhanced product properties. The viscosity of the coating material is a major factor in the speed at which fabric can be coated in a melt calendering operation. By providing lower viscosities of the coating material, the present invention can be used to increase the rate of fabric coating and thus reduce the manufacturing cost. The viscosity of the coating material also has an effect on the forces that tend to push the calendering rolls apart. This action tends to produce differences in the thickness of the coating delivered to the fabric substrate. Coating produced at the center of the roll tends to be thicker than the coating at the edge of the roll. Lowering the viscosity of the coating fluid will reduce this difference and thus lead to a fabric with a more uniform coating.
The lowering of viscosity can also be used to increase the physical properties of the final coated fabric. Very high molecular weight polyolefins have physical properties, such as strength, which make them desirable as fabric coatings. In conventional melt processing their viscosity would be too high to allow fabric coating, without resorting to temperatures which would degrade the polymer and the fabric. Such a very high molecular weight polyolefin can be formulated into a coating fluid with an acceptable viscosity using this invention.
The resulting cured system would have enhanced physical properties, in part due to the elevated molecular weight of the base polymer, and in part due to the benefit obtained from the chemical bonding and polymerization of the liquid components during curing. These improvements in the base properties of the base polyolefin would include any combination of improved impact strength, stronger bonding to the fabric, improved printability and paintability, and better abrasion resistance.
Extrusion coating is a common technique used to apply a polymeric material to a fabric substrate. This process typically involves the generation of a high temperature melt that is forced through a die at a high shear rate. The dies needed to coat wider sheets, such as two meters in width, require the polymer melt to undergo high temperature and a high shear rate. This requires high pressure and expensive equipment. This process can also lead to polymer degradation.
The present invention greatly reduces the temperature, pressure and shear rate requirements needed to practice extrusion coating. This has the benefit of allowing the use of less expensive equipment and reduces the possibility of degradation of the polymeric system due to exposure to excessive temperature or shear rate. As in the calendering case, the physical properties of the resulting polymer coated fabric can be enhanced through the use of higher molecular weight polymers than would be possible to use in the conventional process.
The resulting cured system would have enhanced physical properties, in part due to the elevated molecular weight of the base polymer, and in part due to the benefit obtained from the chemical bonding and polymerization of the liquid components into a superior cross-linked network during curing.
EP AO 605 831, dated Jul. 13, 1994 to Mitsubishi Petrochemical Co. discloses the use of a copolymer of ethylene derived from using metallocene catalyst for food wrap stretched films, with specific thicknesses and properties.
WO A 94 09060, dated Apr. 28,1994 to Dow Chemical Co. discloses the use of metallocene catalyst derived linear ethylene polymers as a film for packaging purposes, with specific additives and properties.
WO A 96 04419, dated Feb. 15,1996 to Forbo-Nairn Ltd. discloses the use of single-site catalyzed polyalkene resin with various additives for the production of sheet materials for rigid floor coverings. It has now been discovered that metallocene catalyzed polyolefins in combination with a different liquid monomer components can be formulated with additives into superior flexible coated fabric products.
WO A 96 11231, dated Apr. 18, 1996 to Henkel discloses a mixture of polymers and unsaturated carboxylic acids, alcohols with plasticizers which are not dissolved in the polymer phase below the film forming temperature. Whereas the current polymer/monomer (P/M ) invention is devoid of a plasticizer.